A color picture tube includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of a faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. An apertured mask, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube faceplate. A focus mask comprises a dual set of conductive lines that are perpendicular to each other and usually separated by an insulative layer. Both shadow masks and focus masks can be constructed in the form of tensioned masks. A tensioned mask is a stretched mask that is maintained under tension by a support frame.
The frame used with a tension mask must have high compliance, both to keep the tensioned strands of the mask tight and to prevent over-stressing of the strands when the mask and its support frame encounter a range of temperatures during processing and tube operation. One existing design relieves mask tension during tube processing by bending of the side members of the frame. However, this design may result in a large variation in compliance between the center and sides of the mask. Such variation occurs because of uneven bending and twisting in the frame members, which ultimately causes a reduction in wire tension in some parts of the mask relative to the tension in other parts. Although tubes with such mask frames have found wide consumer acceptance, there is yet a need for further improvement in tubes, to reduce the weight and cost of the mask-frame assemblies used therein, while providing a compliant structure that is very resistant to bending and twisting.